Packaging containers of the single-use disposable type, in particular such packages for the storage of liquids, are often produced from a packaging material including a core layer of paper which is coated with thermoplastic material and aluminium foil. The packaging material is often provided in the form of webs rolled onto magazine reels, the webs, after being paid out from their magazine reels, being reformed by folding into packaging containers in automatic packaging machines. A commonly occurring package of this type is that which is marketed under the Trademark TETRA BRIK® and which is preferably employed for liquid contents such as milk, fruit juice, etc. This package is produced in automatic packaging and filling machines in such a manner that the web paid out from the magazine reel is reformed into a tube by the edges of the web being united in an overlap seam or joint, whereafter the thus formed tube is filled with the intended contents and separated into individual packages by repeated transverse seals disposed in spaced apart relationship from one another and at right angles to the tube. Once the supplied contents have thus been enclosed in sealed sections of the tube, these sections are separated from the tube by incisions in the above-mentioned transverse sealing zones. The separated tube sections are thereafter formed by folding along crease lines disposed in the packaging material, to form packaging containers of the desired configuration, for example, parallelepipedic containers.
Packages of this type are often fitted with opening arrangements in the form of holes, apertures or slits made in the packaging material and covered by tear-off strips which are normally entitled “pull-tabs”. When the contents consist of a sterile product such as sterilized milk or of an acidic product such as, for instance, orange juice, the package is often manufactured from a packaging laminate which includes an aluminium foil layer making the package extremely tight to penetration by gases such as, for example, oxygen gas which might oxidize the contents of the package with resultant deterioration in quality. In order to achieve the desired tightness, it is of major importance that the aluminium foil layer is not ruptured or damaged in the package forming operation or on manufacture of the packaging material. In addition, for the function of the pull-tab opening, it is vital that the aluminium foil layer possesses extremely good adhesion at the region around the opening hole over which the pull-tabs are arranged to be applied (in a manner which will be described in greater detail hereinbelow) since otherwise the opening operation might easily be unsuccessful, since the covering strip which has been applied over the intended opening can be torn off without the inside coating of plastic and aluminium foil being properly opened.
One object of the present invention is to treat and prepare in a simple and efficient manner a packaging material web of the above-outlined type in such a way that the edge of the packaging material web is effectively sealed off with an upper plastic film disposed around the edge zone. It is known in the art to seal-off liquid absorbent material edges exposed to the inside of a packaging container with thermoplastic strips which overbridge or are folded around such edges. It is also known in the art, with the same purpose in view, to provide the packaging material web with a so-called fixed edge strip of plastic, i.e., with a plastic strip which projects from the web edge of a cardboard web and which may be folded around the edge and sealed against its opposing side. Such a “fixed edge strip” is obtained by disposing cardboard webs beside one another so that a slot or gap is formed between the webs, whereafter the webs and these slots are jointly covered over with a plastic foil or, in certain cases, with a plastic foil and an aluminium foil, whereafter the covered webs are separated by the means of an incision in the region of the slot for forming a projecting, fixed strip. One drawback has hitherto been that it has not been possible to achieve adhesion—or in any event only poor adhesion—between, for example, an aluminium foil layer and a plastic layer in the region of such slots, since the aluminium foil and the plastic layer cannot be compressed together within the region of the slot or incision and particularly not adjacent the defining edges of the slots because of the differing thicknesses of the material and the consequential difficulty for the pressure rollers to compress together the material within the region of the slot. However, employing the process according to the present invention, this drawback is obviated in that a plastic/aluminium foil layer is first produced in which the components in the laminate display good adhesion to one another, and this plastic/aluminium foil layer is then laminated to the above-mentioned side-by-side disposed webs of the core material layer which includes paper or cardboard.
Using prior art technology, packaging material of the type considered here can be produced by applying, in a plurality of separate lamination operations, the different layers—i.e. the aluminium foil layer, the inner plastic layer and so on to the core layer of paper or cardboard, and such a lamination process functions excellently in those cases when the core layer is not provided with holes, apertures or slots, i.e. the regions where the coating layers extend over or beyond edge zones of the core layer. It has proved that difficulties arise, in coating an aluminium foil against a core layer web of paper or cardboard in which the core layer is provided with holes, apertures or slots, in that the aluminium foil must, in connection with the lamination (in which the bonding lamination layer often consists of a thin extrudea thermoplastic film) be pressed against the core layer substrate with the aid of a nip roller or soft pressure roller in order that sufficient adhesion between the aluminium foil layer and the core layer can be achieved. Since, in general, the aluminium foil layer is extremely thin (of the order of approx 5 to 10μ), it will be forced by the nip roller against the edges around the apertures or the slots in the core layer and be partly pressed into these holes or apertures. Since the punched holes, apertures or the like have a relatively sharp edge, there is a risk that the aluminium be ruptured, and in any event the risk occurs that the aluminium foil will become creased around the edges of the apertures or slots and will thereby either be weakened or suffer from poor adhesion between the aluminium foil and the core layer precisely in the edge zones of the holes or apertures. Further, the adhesion between the plastic layer and the aluminium foil layer will be poor in the region of these holes or slots, since the pressure of the nip roller in such regions is limited because of the material thickness reduction in the holes or slots.
These circumstances have constituted a serious problem which, first, has caused ruptures in the aluminium foil layer and thereby insufficient gas tightness in the finished packages, secondly a defective opening arrangement because of poor adhesion between the aluminium foil layer and the core layer in the edge zones around the apertures, and thirdly poor adhesion between the aluminium foil layer and the plastic layer along those parts where the aluminium foil layer and the plastic layer project out beyond the core layer and, thus, receive no support from the core layer during the compression operation.